In order to make vehicle seats comfortable, it is known to provide a lumbar support, i.e. a device arranged within a backrest and comprising a rest member which is coupled to a backrest frame and defines a shaped front surface placed at the lumbosacral area of the body occupying the seat.
Typically, the lumbar support also comprises an adjustment device, which is operable by the user for adjusting the shape and/or position of the rest member according to personal anatomy conformation of the body and/or personal comfort needs.
The tendency is also known in producing lumbar supports that contribute to the security of who occupies the seat, in the event of an accident with a rear impact against the vehicle. This type of lumbar support comprises a rest member that is able to backwardly move in the case of an accident with rear impact, so as to let the user's body approach the headrest of the seat in order to limit the so-called “whiplash” phenomena to the neck (this feature is commonly referred to as “anti-whiplash”).
In this context, the solution proposed in the European Patent EP2199147 is extremely simple and has a low number of components. During operation, this solution enacts an over-centre activity, i.e. the rest member is connected to the seat frame by means of elastic members designed to keep the same rest member in an advanced balanced position or in a rear balanced position. In particular, the elastic members shift between two stable configurations when a certain strength threshold is exceeded. Practically, under normal driving conditions the elastic members tend to maintain the rest member in the advanced balanced position acting as a normal support spring, when the inertia thrust of the rest member exceeds the aforesaid threshold of strength, the elastic members shift back instantly displacing the rest member into the rear balanced position.
The tests on the solution just described have shown that, in use, there may be a shifting of the elastic members even in the absence of an actual accident, so that the driver must take the vehicle to maintenance to restore the elastic members to their original configuration and, accordingly, the rest member in the advanced balanced position.